This is why all the celebrities are wearing blue ribbons on the Oscars red carpet.

There’s one accessory dominating the arrivals of Hollywood’s elite – and it’s for a very good reason.

Celebrities including Best Actress nominee Ruth Negga, model Karlie Kloss and Lin-Manuel Miranda are wearing a blue ribbon to send a very powerful message.

Negga at the Oscars. Image: Getty

According to The Hollywood Reporter, the ribbons are the symbol of the American Civil Liberties Union's new "Stand with the ACLU" initiative.

The campaign is encouraging Hollywood actors and celebrities to sport the ribbon to show they stand in solidarity with the union who work to "defend and preserve the individual rights and liberties guaranteed by the Constitution and laws of the United States".

Support for the ACLU has increased dramatically since Donald Trump's controversial travel ban, with its membership doubling to over one million in the last three months.

The organisation raised $24 million in online donations in the weekend after Trump signed an executive order banning immigrants from seven predominantly Muslim countries. The ban has since been blocked.

It's been a cause Hollywood has rallied for - Sarah Paulson encouraged viewers to donate as she accepted her award for outstanding performance by a female actor in a TV movie or limited series at the SAG Awards, while Casey Affleck wore his ribbon at Saturday's Film Independent Spirit Awards.

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It's a particularly relevant movement for Negga, who is nominated for Best Actress for her role in Loving, a film based on the true story of Mildred and Richard Loving, an interracial couple who were arrested and thrown out of the state of Virgina in the late 1950's.